The invention relates to a printer unit which effects printing on continuous paper such as rolled paper and a printing apparatus incorporating such a printer unit.
In the related art, one type of printing apparatus includes a housing section for housing continuous paper, such as rolled paper, and effects printing by drawing the continuous paper from the housing section. Printing apparatus of this type has an opening section that is opened and closed by a cover. The continuous paper is replaced and the inside of the printing apparatus is maintained through this opening section. When installing or replacing the continuous paper, the printing apparatus entails a necessity of manually drawing the continuous paper from the housing section and setting the thus-drawn continuous paper along a predetermined paper path. It is therefore preferable to locate a print head on the side of the housing and a platen roller disposed in a position opposite to the print head on the side of the cover for opening and closing the opening section of the housing. This configuration assures that the continuous paper can be easily aligned in the paper path when the cover is opened to replace the continuous paper because the platen roller retracts with the cover and thus opens the paper path.
If a thermal print head is used in a printing apparatus, securing of print quality requires accurate positioning of a platen roller with a print line of a print head and pressing of continuous paper against the print line of the print head (with the platen roller). To this end, such a cover of an ordinary thermal printing apparatus is equipped with a pivotable lock lever. The platen roller is positioned by causing the lock lever to engage with the housing.
However, in the related-art printing apparatus, the lock lever is pivotally supported by a lever shaft projecting from the platen frame. The lock lever is engaged with a locking shaft projecting from a head frame. Hence, there is a potential risk of accuracy of positioning of the platen roller with the print head being deteriorated by an error in machining of the platen frame, an error in attachment of the lever shaft to the platen frame, an error in machining of the head frame, and an error in attachment of the locking shaft to the head frame.
It is therefore an object of the invention to provide a printer unit, which enables an improvement in the accuracy of positioning of a platen roller with respect to a print head by minimizing error factors existing between the platen roller and the print head, which obviates a necessity for special lever axis (shaft) or locking axis (shaft), and which enables an attempt for reducing the number of parts and simplifying the structure thereof.
It is also an object of the invention to provide a printing apparatus incorporating such a printer unit.
In order to achieve the above objects, according to the present invention, there is provided a printer unit, comprising:
a print head, provided in a casing of a printing apparatus having a housing section which houses continuous paper therein, and operable to perform printing on the continuous paper;
a platen roller, having a platen shaft rotatably supported on a cover of the printing apparatus which is pivotably supported on the casing to open or close the housing section, the platen roller being abutted against the print head with the continuous paper therebetween and rotated to feed the continuous paper, when the cover is closed;
a head support member, disposed in the casing and pivotably supporting the print head around a head shaft so as to move the print head toward the platen roller; and
a lock lever, which is pivotable about the platen shaft and is engaged with the head shaft to determine a position of the platen roller with respect to the print head when the cover is closed.
Preferably, the head shaft is disposed closer to a pivot of the cover than a printing face of the print head. In such a configuration, since the lock lever is arranged so as not to project from the extremity of the cover, the lock lever is prevented from interfering with opening and closing of the cover, and designing of the cover can be facilitated.
Preferably, an imaginary line passing through an axis of the platen shaft and an axis of the head shaft is substantially parallel with a printing face of the print head when the cover is closed. In such a configuration, positioning of the platen roller with respect to the print head is facilitated, and printing accuracy can be improved by suppressing displacement of the platen roller resulting from driving reaction force.
Preferably, the printer unit further comprises: a platen frame, fixed on the cover, and formed with supporting holes elongated in a direction substantially perpendicular to a printing face of the print head when the cover is closed; and bearing members, through which both ends of the platen shaft is rotatably supported on the platen frame, each of the bearing members being supported by each of the supporting holes movably in an elongating direction of the supporting holes. In such a configuration, since the platen roller (platen shaft) is movable back and forth along with the lock lever, the platen roller can be positioned accurately with respect to the print head without being affected by an error in attachment of the head support member (or a head frame described below) to the casing or the platen frame to the cover.
Here, it is preferable that: the lock lever includes a first engagement member and a first stopper; the platen frame includes a second engagement member and a second stopper; the printer unit further comprises an urging member interposed between the first engagement member and the second engagement member so as to pivot the lock lever in a first direction such that the lock lever engages with the head shaft; and a pivotal movement of the lock lever in the first direction is restricted when the first stopper and the second stopper come in contact with each other.
It is also preferable that the lock lever is formed with a tapered portion which is brought into contact with the head shaft to pivot, for example, temporarily, the lock lever in a second direction opposite to the first direction during a closing operation of the cover.
Further, it is preferable that the head support member is formed with grooves into which the bearing members are respectively fitted when the cover is closed.
Still further, it is preferable that the head support member is formed with projections onto which the bearing members are respectively brought into contact during a closing operation of the cover, so that the print head is temporarily moved away from the platen roller.
Still further, it is preferable that the printer unit as set forth above, further comprises: a head frame, fixed to the casing while pivotably supporting the head support member, the head frame including a first stopper; and an urging member, interposed between the head frame and the head support member so as to pivot the head support member toward the platen roller. The head support member may also further include a second stopper so as to restrict a pivotal movement of the head support member when the first stopper and the second stopper come in contact with each other.
Here, it is preferable that the head frame is formed with grooves into which the bearing members are respectively fitted when the cover is closed.
Further, it is preferable that the head frame includes a guide member which guides the continuous paper into a space between the print head and the platen roller.
Still further, it is preferable that a dimension of each of the bearing members in an axial direction of the platen shaft is greater than an additional thickness of the head frame and the head support member.
Preferably, the lock lever includes a lock releaser which disengages the lock lever from the head shaft.
According to the present invention, there is also provided a printing apparatus incorporating the above described printer unit.
According to the present invention, there is also provided a printing apparatus, comprising:
a print head unit;
a platen unit;
a print head, provided in the print head unit, and operable to perform printing on continuous paper;
a platen roller, provided in the platen unit, having a platen shaft, the platen roller being abutted against the print head with the continuous paper therebetween and rotated to feed the continuous paper;
a head support member, provided in the print head unit, the head support member pivotably supporting the print head around a head shaft so as to move the print head toward the platen roller; and
a lock lever, provided in the platen unit, the lock lever being pivotable about the platen shaft and engaged with the head shaft to determine a position of the platen roller with respect to the print head.